Adhesives have been used for a variety of marking, holding, protecting, sealing and masking purposes. Adhesive tapes generally comprise a backing, or substrate, and an adhesive. One specific type of tape, called a transfer tape, does not comprise a backing, but rather is a standalone adhesive layer. Among the types of adhesives used in tapes, are pressure sensitive adhesives and heat activated adhesives, with pressure sensitive adhesives being the more common.
Pressure sensitive adhesives are well known to one of ordinary skill in the art to possess certain properties at room temperature including the following: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength to be removed cleanly from the adherend. Materials that have been found to function well as pressure sensitive adhesives are polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear strength. The most commonly used polymers for preparation of pressure sensitive adhesives are natural rubber, synthetic rubbers (e.g., styrene/butadiene copolymers (SBR) and styrene/isoprene/styrene (SIS) block copolymers), various (meth)acrylate (e.g., acrylate and methacrylate) copolymers and silicones. Each of these classes of materials has advantages and disadvantages.
Heat activated adhesives are non-tacky at room temperature but become tacky and capable of bonding to a substrate at elevated temperatures. These adhesives usually have a Tg (glass transition temperature) or melting point (Tm) above room temperature. When the temperature is elevated above the Tg or Tm, the storage modulus usually decreases and the adhesive becomes tacky.
Among the adhesive articles that have been prepared are adhesive articles that contain microstructured surfaces. The microstructured surface can be imparted upon the adhesive layer by contact with a microstructured molding tool or microstructured release liner. U.S. Pat. No. 5,650,215 (Mazurek et al.) teaches methods for preparing pressure sensitive adhesives with microstructured surfaces. The microstructured surfaces can provide such useful properties as temporary repositionability, permanent repositionability, and self-debonding.